The Eixample is the most rational grid in Europe with the least rational building in the world dropped into the middle of it. This walk runs three kilometres straight up the seam between the two: Gaudí's Sagrada Família at the bottom, Domènech i Montaner's hospital at the top, and the engineer Ildefons Cerdà's chamfered blocks holding it all in line.
Start early, with a timed ticket bought days ahead — the basilica is no longer a place you can wander into. Take the Nativity facade first, the one Gaudí saw finished, then circle to Subirachs's stark Passion front. Cross to the park for the reflection, then turn your back on the towers and walk up Avinguda de Gaudí, the one diagonal street in a square city, laid deliberately to link the basilica to the hospital.
The Hospital de Sant Pau is the surprise: a whole town of modernista pavilions in tile and brick, calmer than the basilica and far less crowded. End there, and walk to the metro past one chamfered corner — Cerdà's small idea that shaped a city.
